Abstract
The asparagine-linked oligosaccharides on bovine lutropin (bLH) are unusual, containing GalNAc and sulfate but no galactose or sialic acid. Oligosaccharides from metabolically radiolabeled or purified bLH consist of non- (neutral), mono- (S-1), and di- (S-2) sulfated structures. We have previously shown that S-2 is a complex type oligosaccharide bearing two peripheral branches with the sequence SO4----GalNAc----GlcNAc attached to a typical Man3GlcNAc2 core (Green, E.D., van Halbeek, H., Boime, I., and Baenziger, J.U. (1985) J. Biol. Chem. 260, 15623-15630). We have now characterized the S-1 oligosaccharides on bLH which, in contrast to S-2, consist of several different structures of both the hybrid and complex types. The sulfate on S-1 oligosaccharides is located exclusively within the peripheral sequence SO4----GalNAc----GlcNAc. The GalNAc bearing hybrid structures, either with or without sulfate, cannot be processed to mono- or disulfated complex oligosaccharides due to the inability of either alpha-mannosidase II or GlcNAc-transferase II to act on GalNAc containing oligosaccharides. Since both Gal and GalNAc are added to oligosaccharides on some pituitary hormones, for example bovine and ovine follitropin and human lutropin, the Gal- and GalNAc-transferases appear to be key elements in regulating the synthesis of sulfated oligosaccharides on bLH and the other pituitary glycoprotein hormones.
Highlights
Theasparagine-linkedoligosaccharides on bovine species on bLH andhave an unusual structure which has not lutropin(bLH) are unusual,containing GalNAcand previously been encountered (4)
Since bothGal andGalNAc are added to oligosaccharides on some pituitary hormones, for example bovine anodvine follitropin and human lutropin, the Gal- and GalNActransferases appear to be key elements in regulating the synthesis of sulfated oligosaccharideson bLH and the other pituitary glycoprotein hormones
TheS-1 tuted GlcNAc (3,6-dimethyl-[3H]GlcNArce)sidues per oligo- oligosaccharides synthesized in the presence of swainsonine saccharide, demonstrating thatGalNAc is the only terminal are exclusively S-l/hybrid-Man[6], since they are sensitive to amino sugar following release of sulfate
Summary
S04-GalNAcf114GlcNAc@l-2Manal a From Green et al (4). % of total Asn-linked oligosaccharideson [3H]glucosamine-labeled bLH(see Fig. 1).35% of [3H]glucosaminelabeled bLH oligosaccharides areneutral, and their structures are not shown. Digestion of S-l/hybrid (either Man, S-2 oligosaccharides.Alternatively, S-l/hybrid oligosacchaorMan5) oligosaccharides with 8-N-acetylhexosaminidase rides may be final biosynthetic products,which cannot serve (jack bean) does not release any 3H-amino sugar. TheS-1 tuted GlcNAc (3,6-dimethyl-[3H]GlcNArce)sidues per oligo- oligosaccharides synthesized in the presence of swainsonine saccharide, demonstrating thatGalNAc is the only terminal are exclusively S-l/hybrid-Man[6], since they are sensitive to amino sugar following release of sulfate. SwainGlcNAc. After sulfate removal, periodate destroys thesingle sonine blocks formation of sulfated complex type (S-l/comGalNAc, but none of the 3 GlcNAc residues, confirming the plex and S-2), as well as S-l/hybrid-Man,, oligosaccharides. Periodate destroys thesingle sonine blocks formation of sulfated complex type (S-l/comGalNAc, but none of the 3 GlcNAc residues, confirming the plex and S-2), as well as S-l/hybrid-Man,, oligosaccharides.
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